US Patent 7791444 Balun transformer using a drum-shaped core

A balun transformer includes: a drum-shaped core having a core unit and a pair of flanges arranged on both sides of the core unit; a plurality of terminal electrodes arranged on the flanges; a primary winding wound around the core unit, both ends of the primary winding being connected to the terminal electrodes; and a secondary winding wound around the core unit, both ends and a center tap of the secondary winding being connected to the terminal electrodes, wherein the secondary winding includes a first wire extending from one end to the center tap, and a second wire extending from the other end to the center tap, and the first wire and the second wire are wound around the core unit so as to extend along each other.